In metallic conductor systems, radiation losses, resistive losses in the conductor as well as losses in the surrounding dielectric all reduce the power. Line terminations play an important part in insertion loss because they reflect some of the power. All of these effects can be conceptually modelled as various elements which make up the equivalent circuit of the line (see distributed and lumped element models).In an optical fiber system, insertion loss is introduced by things such as connectors, splices, and couplers. Electronic filtersInsertion loss is a figure of merit for an electronic filter and this data is generally specified with a filter. Insertion loss is defined as a ratio of the signal level in a test configuration without the filter installed (V1) to the signal level with the filter installed (V2). This ratio is described in dB by the following equation:

Filters are sensitive to source and load impedances so the exact performance of a filter in a circuit is impossible to precisely predict. Comparisons, however, of filter performance are possible if the insertion loss measurements are made with fixed source and load impedances and 50? is the typical impedance to do this with. This data is specified as common-mode or differential-mode. Common-mode is a measure of the filter performance on signals that originate between the power lines and chassis ground, where as differential-mode is a measure of the filter performance on signals that originate between the two power lines. Link with Scattering parametersInsertion Loss (), could also be computed using scattering parameters:

Since insertion loss is, by definition, a loss (or, negative gain), the leading negative sign is often neglected in microwaves documents like datasheets. ReferencesFederal Standard 1037CCategories: Communication engineering(and so on)